I've read some conflicting posts about what fluid to use in the steering idler. Mine was pretty much empty and smelled like fish oil! I think there was a post that this is what Fiat put in so it was probably never filled up in 30+ years.

I put 80W90 differential oil in there (the same stuff I used in the steering box). But other posts suggest automatic transmission fluid (ATF) because the steering idle is a hydraulic unit. The 80W90 gear oil would be too thick. If it's ATF are there different viscosities for ATF fluid? Or is any ATF for import vehicles fine? And someone mentioned a tablespoon of stop leak because the ATF fluid is fairly thin and I don't want it emptying out through the bottom seal.

I put 80-90 gear lube in both units in Jan 13. No leaks or other problems. My idler was dry with some sediment. Steering wheel vibrations and road bumps are more dampened.

I'm going to run it with 80-90 gear lube (mainly because it's already in there and closed up) and if I find it too stiff then switch to ATF and see what difference it makes. Luckily the idler fluid is easy to change.

I use the 80-90 gear lube too, no complaints.

I also used gear oil. Thinner might be better if in perfect condition, but I would be concerned with leaks on a 40 year old one.